Effects of Loosely Bound EPS Release and Floc Reconstruction on Sludge Dewaterability Haifeng Zhang & Xin Lu & Lianfa Song & Lanhe Zhang Received: 12 September 2017 /Accepted: 29 December 2017 # Springer International Publishing AG, part of Springer Nature 2018 Abstract Loosely bound extracellular polymeric sub- stances (LB-EPS) are highly hydrated biopolymers and play important roles in sludge biofloccualtion and dewaterability. Disruption or solubilization of LB-EPS will promote the alternation of sludge structure and the release of trapped water. In the present study, ultrasonication was employed to extract LB-EPS into the supernatant and release trapped water within them. Excellent performance in enhancing ultrasonicated sludge dewatering was observed under the combined Fe 3+ (20 mg/g dry sludge (DS)) and Ca 2+ (30 mg/g DS) addition. The above fact highlighted the probability to enhance the sludge dewaterability by the dosage of small amount of cations. Further, the combined effects of ultrasonication and multivalent cation addition on floc regrowth on sludge dewaterability were investigat- ed and the possible mechanisms involved in the reorga- nization of sludge structure and the biofloccualtion pro- cess were also explored. In conclusion, the combination of ultrasonication and multivalent cation addition was promising to improve sludge dewaterability. Keywords Activated sludge . Extracellular polymeric substances . Bioflocculation . Multivalent cations . Sludge dewaterability Nomenclature WWTP Wastewater treatment plants EPS Extracellular polymeric substances LB-EPS Loosely bound EPS TB-EPS Tightly bound EPS SEPS Soluble EPS MBR Membrane bioreactor TSS Total suspended solids VSS Volatile suspended solids SRF Specific resistance to filtration BSA Bovine serum albumin RH Relative hydrophobicity MW Molecular weight DS Dry sludge 1 Introduction Biological wastewater treatment processes produce large quantities of excess sludge with a water content of 90%, and thus, the treatment and disposal of excess sludge become a major issue in wastewater treatment plants (WWTP). Chemical conditioning with the addi- tion of flocculants was a routine method to improve the Water Air Soil Pollut (2018) 229:27 https://doi.org/10.1007/s11270-017-3683-z Zhang Haifeng and Lu Xin are co-first authors. H. Zhang : X. Lu : L. Zhang (*) School of Chemistry Engineering, Northeast Electric Power University, Jilin 132012 Jilin, People’ s Republic of China e-mail: zhangbuleriver@163.com H. Zhang : L. Song Department of Civil, Environmental, and Construction Engineering, Texas Tech University, Lubbock, TX 79409-1023, USA H. Zhang : X. Lu : L. Song : L. Zhang School of Civil and Architecture Engineering, Northeast Electric Power University, Jilin 132012 Jilin, People’ s Republic of China